1. Field of the Invention
The present invention relates generally to field of fiber optics and in particular, to pump-combining systems and techniques for use in multicore fiber transmissions.
2. Background Art
Transmissions over multicore fibers (MCFs) have been successfully demonstrated, and are being proposed for various optical communications systems. The ultimate success of MCF-based transmission systems will depend, in significant part, on the development of network components for use with MCFs.
Fiber amplifiers are important components in typical optical transmission systems. A fiber amplifier comprises a length of optical fiber that has been doped with a rare-earth dopant; such as erbium. Light at a first wavelength (e.g., 980 nm) that is launched into the fiber is absorbed by the rare-earth dopant ions, which then emit light at a second, longer wavelength (e.g., 1550 nm). Thus, launching a combined light into the fiber, comprising both a pump light at the first wavelength and a signal light at the second wavelength, results in amplification of the signal light.
Successful multicore transmission fibers and amplifier fibers have already been developed having six or more cores. There is a continuing effort to develop multicore fibers and devices with improved performance and a greater number of cores.
Coupling is a significant issue in the development of successful multicore fiber amplifiers. In a low-crosstalk amplifier, each, core of a transmission multicore fiber must be connected to a corresponding individual core of an amplifier multicore fiber. In addition, pump light must also be launched into the amplifier multicore fiber.
A successful coupling solution should address both performance and cost. Although coupling solutions have been developed for single-core transmission systems, these structures are not readily adaptable to multicore transmission systems. Current proposals for multicore coupling schemes from a number of drawbacks, including high attenuation, high cost, and complexity. There is thus a need for simple, low-loss coupling structures and techniques suitable for use with multicore transmission fibers, multicore amplifier fibers, and pump light inputs.